Panama was (and is) a flag of convenience for many major merchant ship companies, including those of Britain and the USA. Other ships were chartered by the Allies from Panama-flagged neutral countries.
You will find Panama-flagged ships randomly scattered through convoys in NYGM TW 2.0, and all may be safely sunk for tonnage without penalty. I don't know whether this rule applies to other mods.
Stiebler.
NYGM Tonnage War Mod - Leading Edge Realism